Pumping blood in an extracorporeal blood circulation system comprising a centrifugal pump is known, for example, from DE 39 35 502 A1. In these devices, a venous hose line conveys the blood from the patient to the pump and an arterial hose line conveys the blood away from the pump. Since, in these devices, the centrifugal pump is directly connected to the venous inflow line, an excessively high vacuum may occur in the venous hose line if the suction power of the pump is too high, which leads to the blood being damaged. In order to prevent this, the vacuum can be detected on the suction side of the pump by means of a sensor so as to initiate suitable countermeasures against an excessively high vacuum upon reaching a predetermined value, for example by alerting an operator or automatically intervening in the pump operation.
However, detecting the vacuum on the venous side of the pump is problematic since owing to the vacuum prevailing here (as compared to the atmospheric pressure), air could penetrate into the blood circulation system if leaks occur at the site of the pressure sensor. Detecting air penetrating the system as a result of this problem is not practicable; at the same time, air which enters the extracorporeal blood circulation system represents a significant danger to the patient.
Against this background, the problem forming the basis for the invention is to specify a manner in which a reliable value corresponding to the amount of vacuum on the suction side of the pump can be obtained without using a pressure sensor on the venous side of the pump for this purpose.